1. Field of the invention
The present invention relates to a paint discharge control device for use in a painting apparatus.
2. Description of Relevant Art
When painting an automobile body or other objects, the rate of discharge of the paint from a paint coating machine is required to be adjusted dependent on desired coatings. If a smaller area is to be painted or a thinner coating is desired, then the paint should be discharged at a lower rate. If a larger surface is to be coated or a thicker coating layer is desired, a higher paint discharge rate should be selected.
One conventional way for such paint discharge rate adjustment has been to use an air-driven regulator placed in a paint feed passage. The regulator includes a chamber defined by enlarging a portion of the paint feed passage, the chamber being divided by a diaphragm into an air chamber and a paint chamber communicating with a high-pressure paint tank. The paint is supplied from the paint tank by intermittently opening and closing the passage between the paint tank and the paint chamber under the pressure difference between the air chamber and the paint chamber. The rate of pulsations of the diaphragm is varied by changing the air pressure supplied to the air chamber.
In the conventional arrangement, therefore, the air pressure for operating the diaphragm is varied for controlling the rate of discharge of the paint.
By controlling the paint discharge rate with air pressure variations, the paint discharge rate is proportional to the air pressure applied to the diaphragm as indicated by the broken line (b) in FIG. 5 of the accompanying drawings.
The efficiency of a painting process for painting an automobile body, for example, can be increased by abruptly increasing the rate of discharge of the paint. To achieve such an abrupt rate increase, there has been proposed a painting apparatus having a high-rate discharge regulator, in addition to an ordinary low-rate discharge regulator, for abruptly changing the rate of paint discharge. The rate of paint discharge under the air pressure controlled by the high-rate discharge regulator is indicated by the broken line (c) in FIG. 5. The curve (c) shows that fine adjustment of the discharge rate is difficult to attain below the rate 50 cc/min. The paint coated by the high-rate discharge regulator tends to suffer color irregularities. Further, the painting apparatus is complex in construction and cannot easily be controlled.